The emerging label switched networks, such as multi-protocol label switching (MPLS) networks and wavelength division multiplexing (WDM) networks, enable network service providers to route bandwidth guaranteed paths between customer sites. The basic label switched path (LPS) routing is often enhanced using restoration routing, which sets up alternate LSPs to guarantee uninterrupted network connectivity in case network links or nodes fail.
There are two variants of restoration routing. A first restoration technique is known as global (i.e., “end-to-end”) restoration, which provides two disjoint paths between an ingress (source) node and an egress (destination) node. Resources are always reserved on the restoration path and are guaranteed to be available when the restoration path is activated. In an event of a failure along the primary path, the source node detects the failure in the primary path and activates the restoration path. In the absence of an explicit signaling protocol, the source node learns of link failures via intra-domain routing updates such as open shortest path first (OSPF) link state advertisements (LSA) packets or IS-IS Link State Packets (IS-IS LSP), which are processed in the slow-path typically in a routing daemon in the router or switch controller. Such packets are typically generated by timer driven events. This causes very large restoration latencies of the order of seconds or at best 100 s of milliseconds.
In particular, the restoration latency in the case of end-to-end restoration comprises the sum of three components. A first component is the amount of time elapsed before link owner node detects link failure. This is typically of the order of 100 s of microseconds. A second component is the time required for the OSPF or IS-IS routing daemon or fault propagation protocol daemon at the link owner to learn of the link failure and issue a routing update. A third component is the amount of time elapsed before routing or fault propagation protocol updates, which are sent by the link owner, propagate to the source node and a corrective action is taken. This delay depends on network topology and load and can be in the order of seconds. Accordingly, the second and third components of end-to-end restoration are variable and difficult to bound.
A second restoration technique is known as local restoration. Local restoration finds a set of restoration paths that protect the links along the primary path. Local restoration can minimize the need for the source node to be involved in the path restoration, and thereby achieve fast restoration. In particular, in a true local restoration scenario, the delay before corrective action is taken equals the amount of time elapsed before a link owner node detects the link failure. Accordingly, local restoration is attractive since it can meet stringent restoration latency requirements that are often of the order of 50 ms, which is similar to existing SONET protection mechanisms.
However, a link owner may not have capabilities of providing restoration during a link failure. That is, the node may not be designed to provide local restoration or the node may also fail in some manner as to render the node incapable of providing restoration. In this instance, the link owner node will notify the source node of the failure (e.g., using OSPF update messages) in a similar manner as described regarding global (end-to-end) restoration, thereby increasing the latency for routing a message
Moreover, since the local restoration paths use links not on the primary path, additional bandwidth must be reserved that is normally not utilized. The additional bandwidth required is deemed an undesirable cost for providing redundancy. In particular, the additional bandwidth is not normally utilized or used only for low priority traffic, such as best-effort data and under fault conditions, thereby wasting valuable resources that may be otherwise utilized for bandwidth guaranteed data. Accordingly, a method of providing guaranteed bandwidth routing paths with local restoration utilizing minimum bandwidth usage is desirable to reduce the costs of routing information at an economy of scale.